A seat belt attached to a seat for a vehicle is mounted onto a vehicle body by means of a seat belt anchorage. The seat belt anchorage includes a member for supporting the seat to the vehicle body side (hereinafter referred to as “seat support member”). Then, a member for supporting a buckle of the seat belt (hereinafter referred to as “buckle support member”) is provided at the seat support member in such a manner as to be rotatable within a predetermined rotation angle. The buckle support member together with the buckle is called an inner belt. For example, JP2001-180435A discloses an inner belt rotation restriction mechanism.
JP2001-180435A also discloses an inner belt for a passenger seat of a vehicle as a conventional art. The inner belt disclosed includes a stay of which one end is rotatably fixed to a side portion of the seat, and a buckle provided at an end of the stay so as to be engageable with a tongue plate of a seat belt. In order to restrict a rotation of the inner belt in a forward direction of the vehicle, a stopper constituted by being cut and raised is formed at a slide rail attached to the seat in the rear of a rotational axis of the stay so that the stay of the inner belt can make contact with the stopper. As stated above, the cut and raised portion is generally formed in the front or rear of the stay so as to be engageable therewith for achieving an inner belt rotation restriction mechanism. Meanwhile, the inner belt rotation restriction mechanism disclosed in JP2001-180435A is constituted by an inner belt including a rotational axis at one end rotatably mounted onto a side frame forming a side portion of a seat cushion for a vehicle and a connecting portion at the other end connected to the seat belt, and a stopper bracket fixed to the side frame in the front of the rotational axis of the inner belt and including a stopper portion outwardly projecting from the side portion of the seat cushion. According to the inner belt rotation restriction mechanism disclosed, an operation of the inner belt is only restricted when the inner belt tilts towards the seat and rotates in the forward direction and otherwise is not restricted.
According to the aforementioned rotation restriction mechanism in which the cut and raised portion is formed in the front or rear of the stay, the cut and raised portion or a stopper portion is required to be formed away from a rotational center of the stay. Thus, an arrangement of peripheral components, and the like is restricted or a structure of a peripheral portion is complicated, which may lead to a cost increase or increase in size of the rotation restriction mechanism.
Thus, a need exists for a seat belt buckle rotation angle restriction mechanism which is not susceptible to the drawback mentioned above.